Showing papers on "Dynamic Vibration Absorber published in 2001"

Magnetorheological elastomers in tunable vibration absorbers

Abstract: Filling an elastomeric material with magnetizable particles leads to mechanical properties -shear moduli, tensile moduli, and magnetostriction coefficients - that are reversibly and rapidly controllable by an applied magnetic field. The origin of the field dependence of these properties is the existence of field-induced dipole magnetic forces between the particles. These 'smart' composites, which are sometimes termed magnetorheological (MR) elastomers, have been explored for use in a number of components, including automotive suspension bushings. In these and other applications, the tunability of the stiffness can enhance the compliance-control or vibration-transfer performance of the complex mechanical systems in which they are used. In the present study, we have constructed a simple one-degree-of-freedom mass-spring system - an adaptive tuned vibration absorber - that utilizes MR elastomers as variable-spring-rate elements. This device was used not only to explore the performance of such tunable components, but also to extend measurements of the shear moduli of these materials to higher frequencies than has previously been reported. We find that the field-induced increase in moduli of these materials is effective to mechanical frequencies well above 1 kHz, and that the moduli are consistent with the behavior expected for filled elastomers.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Level Flight Trim and Stability Analysis Using Extended Bifurcation and Continuation Procedure

Abstract: 3Hollkamp, J. J., “Multimodal Passive Vibration Suppressionwith Piezoelectrics,” AIAA Paper 93-1683, 1993. 4Hollkamp, J. J., and Starchville, T. F., “A Self-Tuning Piezoelectric Vibration Absorber,” Journal of Intelligent Materials Systems and Structures, Vol. 5, No. 4, 1994, pp. 559–566. 5Rew, K.-H., Han, J. H., and Lee, I., “Adaptive Multimodal Vibration Control of Winglike Composite Structure Using Adaptive Positive Position Feedback,” AIAA Paper 2000-1422, 2000.

Flow-Induced Vibration of Power and Process Plant Components: A Practical Workbook

Abstract: Units and dimensions the kinematics of vibration and acoustics fundamentals of structural dynamics vibration of structures in quiescent fluid 1 - the hydrodynamic mass vibration of structures in quiescent fluids 2 - simplified methods vortex-induced vibration fluid-elastic instability of tube bundles turbulence-induced vibration in parallel flow turbulence-induced vibration in cross-flow axial and leakage-flow induced vibrations impact, fatigue and wear acoustically induced vibration and noise signal analysis and diagnostic techniques.

Experimental study on an impact vibration absorber

Abstract: This paper investigates the effects of mass ratio, clearance, and excitation amplitude on system dynamics and impact vibration absorber (IVA) effectiveness. The experimental studies were carried out for both free and forced vibrations. For free vibrations, the effects of system parameters on the rate of decay of vibrations were shown. Constant frequency and frequency sweep experiments were conducted to study the dynamics of the system under forced vibration. Optimum system parameters were extracted, for which the vibration absorption and absorber efficiency is greatest. It was also shown that phase plots and coherence, between the forcing function and the primary system response, offered an insight in the effectiveness of the IVA.

The Effects of Different Input Excitation on the Dynamic Characterization of an Automotive Shock Absorber

Abstract: This paper deals with the dynamic characterization of an automotive shock absorber, a continuation of an earlier work [1]. The objective of this on-going research is to develop a testing and analysis methodology for obtaining dynamic properties of automotive shock absorbers for use in CAE-NVH low-to-mid frequency chassis models. First, the effects of temperature and nominal length on the stiffness and damping of the shock absorber are studied and their importance in the development of a standard test method discussed. The effects of different types of input excitation on the dynamic properties of the shock absorber are then examined. Stepped sine sweep excitation is currently used in industry to obtain shock absorber parameters along with their frequency and amplitude dependence. Sine-on-sine testing, which involves excitation using two different sine waves has been done in this study to understand the effects of the presence of multiple sine waves on the estimated dynamic properties. In an effort to obtain all frequency dependent parameters simultaneously, different types of broadband random excitations have been studied. Results are compared with stepped sine sweep tests. Additionally, actual road data measured on different road profiles has been used as input excitation to obtain the shock absorber parameters for broad frequency bands under realistic amplitude and frequency conditions. These results are compared with both simulated random excitation and stepped sine sweep test results. INTRODUCTION The shock absorber is one of the most important elements in a vehicle suspension system. It is also one the most non-linear and complex elements to model. The current method of characterizing the dynamic properties of shock absorbers for CAE models involves testing at discrete frequencies, displacements, and preloads using an MTS test machine. The dynamic stiffness (K) and damping (C) are extracted by fitting a linear model of the form F(ω)=K*x(ω)+C*v(ω) to the measured input displacement (x), velocity (v), and output force (F). The excitation technique is a pure sine excitation at the desired frequency and amplitude. These harmonic excitations are then swept through all desired frequency and amplitudes. Parametric and non-parametric models also exist for the shock absorber. A non-parametric model based on a restoring force surface mapping has been developed [2,3,4]. The model considers the force to be a function of displacement and velocity. Although, this model is more applicable to a single frequency excitation, it serves as a useful tool for identifying the non-linearity’s in the system. A comprehensive physical model was developed by Lang [5], later condensed and validated by Morman [6]. Lang’s model has more than 80 parameters, is computationally complex and is not suitable for comprehensive vehicle simulation studies. Morman’s model has been shown to be useful for studying the effects of design changes for a particular shock. Reybrouck [7] has developed a physical model, which has 14 parameters, valid for frequencies up to 20 Hz, but has limited appeal for the analysis of shock absorbers for NVH applications.

Passive vibration absorber with dry friction

Abstract: The properties of a passive vibration absorber with dry friction significantly differ from those of the classical linear absorber. The exceptional phenomenon is the possibility of suppressing all excited modes. This effect is influenced to a small extent by a special shape of the friction characteristic, but mainly by an appropriately adjusted threshold of the static friction. The theoretical predictions are confirmed by experimental investigations.

Performance of Nonlinear Vibration Absorbers for Multi-Degrees-of-Freedom Systems Using Nonlinear Normal Modes

Abstract: Linear vibration absorbers are a valuable tool used to suppress vibrations due to harmonic excitation in structural systems While limited evaluation of the performance of nonlinear vibration absorbers for nonlinear structures exists in the literature for single mode structures, none exists for multi-mode structures Consequently, nonlinear multiple-degrees-of-freedom structures are evaluated The theory of nonlinear normal modes is extended to include consideration of modal damping, excitation and small linear coupling, allowing estimation of vibration absorber performance The dynamics of the N + 1-degrees-of-freedom system are shown to reduce to those of a two-degrees-of-freedom system on a four-dimensional nonlinear modal manifold, thereby simplifying the analysis Quantitative agreement is shown to require a higher-order model which is recommended for future investigation

Dynamic vibration absorber for a disk player

Abstract: A dynamic vibration absorber for a disk player includes a deck base, a deck plate movably disposed on the deck base to support a spindle motor that spins a disk, a mass body disposed around the deck plate, and a flexibly changeable connection member that connects the deck plate and the mass body. A dynamic vibration absorber including the mass and connection member reduces vibration generated when the disk spins using a reciprocal action of the mass body and the connection member relative to the deck plate.

Modal Overlap and Dissipation Effects of a Cantilever Beam with Multiple Attached Oscillators

Abstract: This work was prompted by a study performed by Strasberg [7] in which numerous small spring-mass-damper systems are attached to a large suspended mass representing the master structure. The isolated natural frequency of each attached system was selected to match in average the natural frequency of the isolated master structure, Strasberg found that the critical issue when an impulse excitation is applied to the master structure is the bandwidth of the isolated attached systems in comparison to the spacing between the natural frequencies of the system. Modal overlap, which corresponds to bandwidths that exceed the spacing of those frequencies, was shown to greatly influence the response of the master structure. Light damping, for which there is little or no modal overlap, corresponds to an impulse response that consists of a sequence of nearly periodic exponentially decaying pulses, and the transfer function for harmonic excitation of the master structure indicates that the substructure acts as a vibration absorber for the master structure. Increased damping leads to modal overlap, with the result that the impulse response consists of a single decaying pulse. The frequency domain transfer function indicates that the vibration absorber effect is enhanced. The present work explores these issues for continuous systems by replacing the one degree of freedom master structure with a cantilever beam. The system parameters are selected to match Strasberg's model, with the suspended oscillators placed randomly along the beam. The beam displacement is represented as a Ritz series whose basis functions are the cantilever beam modes. The coupled equations are solved by a state-space eigenmode analysis that yields a closed form representation of the response in terms of the complex eigenmode properties. The continuous fuzzy structure is shown not to display the transfer of energy between the master structure and the substructure that was exhibited by the discrete fuzzy structure, apparently because of the asynchronous motion of the attachment points resulting from the spatial variability of the beam's motion. The vibration absorber effect for harmonic excitation is only obtained for the heavy damping in the case of a beam.

Nonlinear Control of Plate Vibrations

Abstract: A nonlinear active vibration absorber to control the vibrations of plates is investigated. The absorber is based on the saturation phenomenon associated with dynamical systems with quadratic nonlinearities and a two-to-one internal resonance. The technique is implemented by coupling a second-order controller with the plate's response through a sensor and an actuator. Energy is exchanged between the primary structure and the controller and, near resonance, the plate's response saturates to a small value. Numerical results are presented for a cantilever rectangular plate. Modal analysis is used to solve for the plate displacement. Finite-element methods are used to extract the eigenmodes of the system. A numerical study is conducted to optimize the location of the actuators to maximize its controllability. In this regard, the control gain is maximized for the PZT actuators. Furthermore, a more general method is introduced, which is based on a global measure of controllability for linear systems.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Airbag module for motor vehicles

Abstract: The invention relates to an airbag module for motor vehicles comprising a housing for an inflatable airbag and a gas generator which is connected to a base element fixed to the module in the assembled state, with the gas generator and the base element being combined to form an assembly serving as a vibration absorber and being unreleasably connected to one another by at least one elastic and/or vibration damping coupling element via which the gas generator is supported over its area at the base element.

Gun barrel vibration absorber to increase accuracy

Abstract: : Gun barrel vibrations lead to dispersion in the shot patterns Thus, reducing these vibrations should lead to increased accuracy. Since the muzzle is the anti-node for all vibration modes and its vibrations have the greatest effect on shot dispersion. it is the obvious location to attempt to dampen the vibrations A model of the gun barrel was created in MATLAB(registered) and verified by modal impact testing. Modal impact testing was done for the barrel alone and for three different muzzle brake vibration absorber configurations. Additionally the gun was fired with and without the absorber to determine its performance. Significant reduction in shot dispersion was observed.

A New Approach to Semi-Active Vibration Suppression using Adjustable Inertia Absorbers

Abstract: Detuning is a common occurrence, which is widely seen in industry and brings sub par vibration suppression performance. This study introduces a semi-active retuning methodology that imparts optimum...

Shock absorber for automobile

Abstract: A shock absorber for an automobile which exhibits a vibration damping effect in a wide range of a frequency, while suppressing generation of frictional noise. The shock absorber for the automobile has a buffer member interposed between parts. The buffer member has a laminated structure including a plurality of vibration damping layers each having a peak of loss tangent tanδ in a range of a frequency which is different from others and surface layers made of thermoplastic resin.

A Nonclassical Vibration Absorber for Pendulation Reduction

Abstract: A passive vibration absorber for reducing the motion of a planar pendulum is developed. The system is excited by the horizontal motion of the support. The design transforms the original one-degree-of- freedom pendulum into a double pendulum by adding a small secondary pendulating sacrificial mass between the main system and the base excitation point and two pretensioned springs that generate negative restoring moments (i.e., of opposite sign to that of the gravity-induced restoring moments). Optimal conditions for enhancing the transfer of energy from the main (lower) to the secondary (upper) pendulum are sought. The damping is assumed to be of a linear viscous-type. Due to the action of the springs, the transfer function between the pendulation angle of the main system and the disturbance, in the undamped linearized case, can be reduced to zero for any excitation frequency This is accomplished by requiring that the two spring stiffnesses satisfy an algebraic tuning relation. Due to the inherent inertial ...

Muzzle brake vibration absorber

Abstract: A muzzle brake vibration absorber for use on a gun barrel is used to store potential energy during gun firing and re-introduce the energy, in part, to the gun barrel out of phase relative to the gun barrel motion. As a result, the deviation of the gun barrel is mitigated to improve the overall accuracy of the gun system. Additionally, the muzzle brake vibration absorber may compliment the functions of a muzzle brake or fuze setting device for the gun system.

Multifrequency piezoelectric vibration absorber for variable frequency harmonic excitations

Abstract: It has been shown that piezoelectric materials can be used as passive electromechanical vibration absorbers by shunting them with electrical networks. Semi-active piezoelectric absorbers have also been proposed for suppressing harmonic excitations with varying frequency. However, these semi- active devices have limitations that restrict their applications. In a previous study, the authors have developed a high performance active-passive alternative to the semi-active absorber that uses a combination of passive electrical circuit and active control actions. The active control consists of three parts: an adaptive inductor tuning action, a negative resistance action, and a coupling enhancement action. This new device has been shown, both analytically and experimentally, to be very effective for the suppression of harmonic disturbances with time-varying frequency. In the present paper, the adaptive active-passive piezoelectric absorber configuration is modified so that it can track and suppress multiple harmonic excitations. The effectiveness of this new multi-frequency absorber design is demonstrated by comparing its performance and control power requirement to a start-of-the-art adaptive feedforward control law.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Assessment of an active dynamic vibration absorber

Abstract: The present paper addresses the attenuation of mechanical vibrations using active dynamic vibration absorbers (DVAs). Besides the typical parameters of passive DVAs (inertia, stiffness and damping), active DVAs possess anactuator placed between the primary mass and the absorber mass, which applies a control force according to an appropriate control law. This way, active DVAs can be tuned to any value of the excitation frequency within a relatively large frequency band by modifying the control force, without any change in the values of the passive parameters. A particular configuration of active DVA is proposed, based on a control law in which the control force is expressed as a linear combination of the relative displacement, velocity and acceleration responses of the DVA mass with respect to the primary system. The basic formulation is first presented, including stability analysis, DVA tuning by frequency response zero placement and optimal frequency response shaping. Finally, the main features and performance of the active DVA are assessed through numerical simulations.

Shock reducer for automobiles

Abstract: The utility model relates to a vibration absorber for automobiles, which comprises a guide positioning steel ball 6 of a piston, the guide positioning steel ball of the piston is inlaid around the circumference of the outer side wall 10 of a piston 3, and a steel jacket 1 is filled with vibration absorber oil 7. The steel jacket is filled with the vibration absorber oil, so, the heat generated by the friction between a piston rod 2 and oil seal 4 is absorbed in time, the hard friction between the piston rod and the oil seal is reduced, and the oil seal and the piston rod can not be damaged in a short time. The friction between the piston and the inner wall of the steel jacket is not direct, so, the piston and the steel jacket are not easy to abrase, the vibration absorber oil filled in the steel jacket can make the movement from top to bottom of the piston in the vibration absorber soft, the vibration absorption effect is good, and three to five years of the integral service life can be reached.

Composite vibration damping system

Abstract: Plural vibration damping devices transmit to and receive energy from a distributor that is programmed to either dissipate the vibration induced energy produced by the devices or redistribute the vibration induced energy produced by some of the devices to minimize overall vibration without introduction of energy from an external source.

Dynamic vibration absorber for rotor and elevator using this absorber

Abstract: PROBLEM TO BE SOLVED: To provide the dynamic vibration absorber that can easily install a rotor, quantitatively and easily design, and easily adjust SOLUTION: A pendulum 10 comprises a rod 13 that is oscillatingly and universally supported at one-rod end on the side part 4 of a rotor 1, and a weight 14 attached to the rod 13 Besides, an elastic bodies 16 press the side part of the rod 13 to turn the rod 13 toward the radial direction of the rotor 1

Liquid enclosed vibration absorber

Abstract: PROBLEM TO BE SOLVED: To provide a liquid enclosed vibration absorber which is applied easily for complex car loading styles, their dimensions and also is assembled easily and gets necessary strength and is improved in durability and reliability. SOLUTION: The rubber vibration absorber body 3 is equipped between the holding cylinder 11 of the lower fitting metal 1 and the upper fitting metal 2. The ring 30 is stuck at the outer surface of lower portion of absorber body 3. The diaphragm 5 is equipped on the bottom of the middle cylinder 4. The partition 6 is equipped on the inner surface of cylinder 4. The top of cylinder 4 is inserted into the lower portion of cylinder 32. The outer edge in top side of middle cylinder 4 is calked and fixed on the flange portion 31 of the ring. The chamber between the partition 6 and the absorber body 3 is liquid chamber 7a and the chamber 7b is between the partition 6 and diaphragm 5. The orifice 8 is connected between the chamber 7a and 7b. The middle cylinder 4 is pressed into the holding cylinder 11. The stopper 9 is equipped over the upper fitting metal 2 and is calked and fixed on the top edge of cylinder 11.

Use of linear and nonlinear vibration absorbers for buffet alleviation of twin-tailed fighter aircraft

Abstract: We investigate theoretically and experimentally the performance of linear and nonlinear vibration absorbers to suppress high-amplitude vibrations of twin-tailed fighter aircraft when subjected to a primary resonance excitation. The tail section used in the experiments is a 1/16 dynamically scaled model fo the F-15 tail assembly. Both techniques (linear and nonlinear) are based on introducing an absorber and coupling it with the tails through a sensor and an actuator, where the control signals ae either linear or quadratic. For both cases, we develop the equations governing the response of the closed-loop system and use the method of multiple scales to obtain an approximate solution. We investigated both control strategies by studying their steady-state characteristics. In addition, we compare the power requirements of both techniques and show that the linear tuned vibration absorber uses less power than the nonlinear absorber.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.